The sport of sailboarding or windsurfing has experienced a tremendous growth in popularity over the past several years. Along with this growth in popularity, there has also been numerous changes in equipment design through the use of, and experimentation with, lighter and stronger materials. Improved equipment permits the user to push the performance limits of the sailboard's ability to sail faster, jump over waves and carve sharper turns. It is also important to the individual sailor that these performance aspects be achieved at an affordable expense and that the equipment is durable so that it can withstand the repeated punishment that these increased performance demands place on the equipment on a regular basis.
It has also been long recognized that the fin and fin box region of the sailboard play a significant part in the sailboard's ability to perform in the water, since all the power of the wind harnessed by the sail must be transmitted through the fin in order to propel the sailboard along the water in the desired direction. Accordingly, there have been a number of attempts to solve the problems particular to sailboard fins and their fin boxes.
A primary problem common to both sailboard and surfboard fins is how to ensure a secure attachment to the underside of the board. A traditional approach is to permanently bond ("glass") the fin to the board with fiberglass and resin. This method has enjoyed an enduring popularity with the surfboard industry, since it provides a simple, light weight and secure fixture. Also, most surfboard shapers use more or less a standard fin design and thus few new surfboards come equipped with a fin box since there is little need to change fin sizes.
But surfboarding is not equivalent to sailboarding. A glassed-in fin is undesirable for use with a sailboard since it limits the interchange of different sized fins, which is of critical importance to a sailboarder. It is not uncommon for a sailboarder to have a quiver of five or six fins which are similar in profile but differ in size so they may be changed according to the wind conditions. Moreover, there are different fin designs intended for rough water, speed, wave riding, flat water recreational sailing, etc.
Channel-type fin boxes are typically shallow (U.S. standard is 25 mm deep and European standard is 33 mm deep) and have a narrow channel or slot width (9 mm being the U.S. and European standard channel width). A problem with these shallow/narrow fin boxes is that they are simply inadequate for windsurfing because of the great potential for the fin box to come loose and break out of the sailboard. If repairable, the repair is very expensive. This problem is due to the increased loads placed on the fin box due to the greater lifting forces associated with the generally larger surface area of the sailboard fins and the increased velocities of the sailboard fins relative to the water.
It is known from Lobe (U.S. Pat. No. 4,846,745) and Lobe (U.S. Pat. No. 4,964,826) to provide a slide plate member in an adjustable fin box which is predisposed to catastrophically fail when the fin is stressed to a limit which would normally cause the fin box to break out of the board, such as when the fin strikes a submerged rock. The slide plate member is normally disposed to be slidingly adjustable within the opposed parallel grooves provided in the inner longitudinal sides walls of the fin box. By permitting the slide plate member to fail first, the fin dangles loosely from the box so that the fin box does not tend to break out of the board. While this approach limits the damage to the most easily replaceable and least expensive component of the fin box system (i.e., the slide plate), the sailboard is left without any turning capability when the slide plate breaks. Also problems still exist with the fin box working itself loose from the board over time from the side stresses placed on the fin box.
Mizell (U.S. Pat. No. 4,379,703) discloses a fin box for use in surfboards wherein the fin box includes a laterally-extended perimeter flange member which interacts with the surrounding foam of the board to aid in the prevention of the fin box from coming loose from the board when the fin (when placed in the fin box) is stressed by a transverse load. The fin box also includes a fin base engagement means comprising a fixed nylon pin disposed in a forward end of the fin box and a steel insert/screw combination place at an angle at a rear end of the box. In use, a notch is provided in the forward end of a modified fin base and is adapted to receive the nylon pin while the rear end of the fin base is secured with the angled insert and screw. The fin box of Mizell, being relatively shallow and narrow in width, is not acceptable for extended use in sailboards since the transverse forces experienced by the fin and fin box of a fast moving sailboard are so much greater than the transverse forces experienced by a slower moving surfboard.
Sheerwood (U.S. Pat. No. 4,904,215) teaches to make a fin box retainer for holding the fin box to the rest of the board by surrounding a conventional plastic fin box made of ABS resin (acrylonitrile-butadiene-styrene copolymer) with a foamable liquid. The retainer is formed first within a mold and is then transferred from the mold and inserted into a prepared grove in the unfinished polyurethane foam board blank after which it is then glassed into place. The foam immediately surrounding the fin box, being approximately twice as dense as the rest of the foam blank, provides much more strength and rigidity for preventing the fin box from breaking out of the sailboard. Mizell does not discuss nor even address the problem of maintaining a firm and secure contact between the fin base and the fin box.
It is also known in the prior art to provide a stronger and more positive contact between the sailboard fin and the fin box by using a "cavity-type" fin box design. In contrast to a standard fin box (dimensions: 3/8" slot width; 7/8" slot depth; 7-8" slot length), the cavity-type box design typically has a wider slot width on the order of 5/8" to 1 1/4" (16 mm to 25 mm), a variable slot depth in the range of 1 1/2" to 2" (38 mm to 50 mm), and a shorter slot length of about 6" (150 mm). With the appropriately dimensioned fin base, these new dimensions provide for a much stronger connection between the fin base and the cavity fin box and break out of the fin box is substantially reduced. Examples of currently commercially available cavity-type fin boxes include: the Tiga Conic Box and the F2 Power Box, both originating from Europe and distributed through FUNSPORT USA of Glendale, Calif.; and the Tuttle Box available through WATERAT SAILING EQUIPMENT of Santa Cruz, Calif.
Of course, the design of the cavity boxes have also required the design and manufacture of a specially designed fin (or "foil") which has a wider and deeper fin base configured to fit snugly within (or "plug in") the cavity. The fin and cavity box are often offered as a "fin system" to the purchaser whereby the specially made foils are sold in combination with sailboards having a cavity fin box.
One disadvantage with switching over to the cavity fin boxes is the increased economic costs involved, considering that the fins or foils for the cavity fin boxes cost about 30% more per fin than standard narrow based fins. At current retail prices, that translates to about a $30.00 difference per fin, since standard sailboard fins sell for about $70.00 retail and the improved foils sell for $100.00 or more. Thus, when a user upgrades his or her sailboard to a model that includes a cavity-type fin box, he will often be left with several useless, out-of-date narrow-based fins.
To get around this situation, some users have resorted to the labor-intensive approach of cutting down the excessive length of their standard narrow base fins and have used the cavity fin box as a mold to construct a permanent "enlarged" fin base to fit within the cavity fin box. Under this approach the user is locked in to using only that particular fin. Should the fin itself fail, a whole new fin and custom fin base must be made. Most fin manufacturers are also reluctant to start producing fins that will fit in the new cavity fin boxes since they are already set up for mass production of standard narrow based fins and expensive new tooling would necessarily be required to modify their standard fin designs to fit cavity fin boxes. Moreover, they would also have to tool up separately for each of the several different types of cavity fin box designs currently in use.
Thus, there is a definite need in the art for a low cost adapter which permits the retrofit use of a standard narrow base fin with a larger cavity-type fin box of a sailboard so that a user does not need to buy a complete new set of expensive fins specially made for a cavity-type fin box. There is also a need for such an adapter whereby the ordinary consumer with minimized technical know-how can perform by himself, any necessary modification to his standard narrow base fin. Further, there is a need for a fin adapter which retains the cavity-type fin box advantages over the prior art standard fin box of improved strength and performance and does not add an appreciable amount of weight to the fin system.